If running a full node for the purpose of helping the network, then I'm a little bit skeptical. A full node should preferably be up 24/7 and for a phone, It should be resource consuming to do so when it comes to the battery and also storage as years go by.
And If by that, it's just so the user is in full control of his transactions unlike with SPV wallets or closed source/centralized ones then, to be honest, I doubt that anyone cares that much. Not to buy another phone anyway.
I would rather go with something like
Bitseed. It's a little bit more expensive, but it does the job perfectly and it's up 24/7 and it also lasts for years to come (1 TBB storage).