java - Call PHP function using Android

I need to call a function in a php file which uses latitude and longitude to calculate the distance moved. Very unsure how to do it, so would love some suggestions.

PS: I know it'd be easier to calculate it without using PHP but unfortunately I am required to do it this way...

Here's my code:

MainActivity.java:

public class MainActivity extends AppCompatActivity {
    private static final String URL = "http://192.168.0.105/location.php";
    private final static int REQUEST_CODE_LOCATION_PERMISSION = 1;
    public Button startButton;
    public TextView distance;
    public double lat1, long1, lat2, long2, latitude, longitude;
    public boolean checkLoc = false;
    public boolean running = false;
    public String locString = "loc1";
    final Handler handler = new Handler();
    int interval = 10000;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        startButton = findViewById(R.id.startButton);
        distance = findViewById(R.id.distView);

        startButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startButton.setEnabled(false);
                running = true;
            }
        });

        if (running = true){
            handler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    if (ContextCompat.checkSelfPermission(getApplicationContext(),
                            Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                        ActivityCompat.requestPermissions(MainActivity.this,
                                new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
                                REQUEST_CODE_LOCATION_PERMISSION);
                    } else {
                        getCurrentLocation();
                    }

                    System.out.println(locString);
                    if (locString.equals("loc1")){
                        lat1 = latitude;
                        long1 = longitude;
                        locString = "loc2";
                    } else if (locString.equals("loc2")){
                        lat2 = latitude;
                        long2 = longitude;
                        locString = "loc1";
                    }

                    if (lat1 != 0 && lat2 != 0){
                    }
                    System.out.println("Lat1: " + lat1 + "\nLat2: " + lat2);
                    handler.postDelayed(this, interval);
                }
            }, interval);
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (requestCode == REQUEST_CODE_LOCATION_PERMISSION && grantResults.length > 0) {
            getCurrentLocation();
        } else {
            Toast.makeText(this, "Permission denied!", Toast.LENGTH_SHORT).show();
        }
    }

    private void getCurrentLocation() {
        LocationRequest locationRequest = new LocationRequest();
        locationRequest.setInterval(10000);
        locationRequest.setFastestInterval(3000);
        locationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);

        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            return;
        }
        LocationServices.getFusedLocationProviderClient(MainActivity.this)
                .requestLocationUpdates(locationRequest, new LocationCallback(){
                    @Override
                    public void onLocationResult(LocationResult locationResult) {
                        super.onLocationResult(locationResult);
                        LocationServices.getFusedLocationProviderClient(MainActivity.this)
                                .removeLocationUpdates(this);
                        if(locationResult != null && locationResult.getLocations().size() > 0){
                            int latestLocationIndex = locationResult.getLocations().size() - 1;
                            latitude = locationResult.getLocations().get(latestLocationIndex).getLatitude();
                            longitude = locationResult.getLocations().get(latestLocationIndex).getLongitude();
                            }
                    }
                }, Looper.getMainLooper());
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu){
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.dist_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()){
            case R.id.meter:
                return true;
            case R.id.km:
                return true;
            case R.id.miles:
                return true;

        }
        return true;
    }



}
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location.php:

<?php
function distance($lat1, $lon1, $lat2, $lon2, $unit) {
    if (($lat1 == $lat2) && ($lon1 == $lon2)) { 
        return 0; 
    }
    $theta = $lon1 - $lon2;
    $dist = sin(deg2rad($lat1)) * 
            sin(deg2rad($lat2)) + cos(deg2rad($lat1)) * 
            cos(deg2rad($lat2)) * cos(deg2rad($theta));
    $dist = acos($dist);
    $dist = rad2deg($dist);
    $miles = $dist * 60 * 1.1515;
    $unit = strtoupper($unit);
    if ($unit == "K") {
        return ($miles * 1.609344);
    }else if ($unit == "N") {
        return ($miles * 0.8684);
    } else {
        return $miles;
    }
}

/*Write the scripts to extract the latitude and longitude from your URL*/
?>
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