Telephonymanager.EXTRA_INCOMING_NUMBER is deprecated in API level 29

As @Saurabh said, the new way to screen calls is through the CallScreeningService. However, for the service to work on Android Q and up, the user needs to set your app as the default caller ID & spam app (which is done by using the new RoleManager class)

1. Register your screening service:

    <service android:name="com.example.ScreeningService"
        android:permission="android.permission.BIND_SCREENING_SERVICE">
        <intent-filter>
            <action android:name="android.telecom.CallScreeningService"/>
        </intent-filter>
    </service>
   

2. Create you service class:

    @RequiresApi(api = Build.VERSION_CODES.N)
    class ScreeningService : CallScreeningService() {
   
        override fun onScreenCall(details: Details) {
            //code here
        }
   
    }
   

3. Request the screening role from the user in your main activity (or where ever you see as fit):

    @RequiresApi(Build.VERSION_CODES.Q)
    private fun requestScreeningRole(){
        val roleManager = getSystemService(Context.ROLE_SERVICE) as RoleManager
        val isHeld = roleManager.isRoleHeld(RoleManager.ROLE_CALL_SCREENING)
        if(!isHeld){
            //ask the user to set your app as the default screening app
            val intent = roleManager.createRequestRoleIntent(RoleManager.ROLE_CALL_SCREENING)
            startActivityForResult(intent, 123)
        } else {
            //you are already the default screening app!
        }
    }
   

4. Catch the user's response:

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
            super.onActivityResult(requestCode, resultCode, data)
            when (requestCode) {
                123 -> {
                    if (resultCode == Activity.RESULT_OK) {
                        //The user set you as the default screening app!
                    } else {
                        //the user didn't set you as the default screening app...
                    }
                }
                else -> {}
            }
        }
   

Apologies for using a hard coded request code >.<

Create a CallScreeningService like this:

class ScreeningService : CallScreeningService() {

    override fun onScreenCall(callDetails: Call.Details) {
        val phoneNumber = callDetails.handle.schemeSpecificPart
        // Do stuff with phone number
    }
}

And register this service in your AndroidManifest.xml:

<service android:name="your.package.ScreeningService"
         android:permission="android.permission.BIND_SCREENING_SERVICE">
     <intent-filter>
         <action android:name="android.telecom.CallScreeningService"/>
     </intent-filter>
</service>

I know it's pretty late but if someone has similar problem I found a solution that works on API 28+ for TelephonyManager. For just identifying phone number CallScreeningService is an overkill, and you could probably override users private settings or another app that blocks spam calls.

You need to add android.permission.READ_CALL_LOG in your manifest and request it in a runtime.

 if (Build.VERSION.SdkInt >= BuildVersionCodes.P) {
            if (ApplicationContext.CheckSelfPermission(Manifest.Permission.ReadCallLog) != Permission.Granted)
            {
                ActivityCompat.RequestPermissions(this, new string[] { Manifest.Permission.ReadCallLog }, ACTION_READ_CALL_LOG);
            }
        }

Provided user allows your app to read call log, after broad cast receiver hits OnReceive => ActionPhoneStateChanged phone number will be empty at the first instance, but second time it should be populated. So be prepared that on Api 28+ phone number could be identified at the second time.