Bill,
I do not know the phone you have, however if it is recent, then it has GPS built in, and most likely turned on if you have not turned it off. Also, if you have a newer phone, you are well above that version (depends on carrier some). Latest version is Android 6. Usually you can get the version by going to Settings->System->Phone Information (or About Phone).
That said, I am one who uses Strelok. They also have a lot of scope reticles in the database (more in the paid version), so you get that as well. I have an Easy MOA & Mil Calculator, however I do not really use it (also free).