[LightX]

More like gaining access, like you would install a backdoor on a computer. Stealing data..ehhh not so much. And since Android is based on linux, then it would be possible, if I understand correctly?

Haha sorry but there is another question needing to be asked now. Is it YOUR phone that you want full access to? Or someone else's? If it is just yours, look up rooting your phone (android) and/or jailbreaking (iPhone)
That will give you full access to your phone and all its files, but unless you physically have the victims phone and a computer without them watching, you cant do that to theirs. Rooting/Jailbreaking if more for the user to have, not something that you would use to hack others.