I have just installed 2 days ago Pi-Hole today for blocking some distraccions for sudiying (YouTube) and I have ad blocking working on Android with Samsung internet explorer, Google Chrome and all apps. I'll explain what I did:
- Set Android pone IP to an static one from the router.
- On the Android Device, go to wifi settings, select your wifi network, advaced settings, set IP to static (check that it is the same static ip you set on router).
- On DNS 1 write the Pi-Hole static IP (I suppose you set Pi-Hole IP to static on router when you did the Pi-Hole installation).
- On DNS 2 write any DNS you like (I have Google DNS 8.8.4.4). This let you to have normal internet when you turn off the raspberry or lost conection for any reason.
Extra: I had everything working at this point but I highly recommend to add more blocking lists, I did it from this (excellent work): [UPDATE] The best blocking lists for the Pi-Hole + Alternative DNS servers 2019
I hope I could help you.
EDIT: More details. I set Google DNS on Pi-Hole. Raspberry model: Pi 3B. Android device: Samsung Galaxy S9+, Android 9.0. I think that Android versión and device's Brand are not the problem but I add this details for more info.