Here is something we can say that iOS is more secure than Android phone. In case of a phone snatch, not only your wallets but your data is also at risk as anyone can get access to the Android phone storage. However, on the other hand, no can login in your iPhone and more importantly no one can reset it unless they have your iCloud password. But regarding the wallets, i don't think it is safe to keep them in either of the phones.
Even though your wallet in your phone is not connected to the internet most of the time, it is certainly not a replacement for a hardware wallet. And it will still be considered a hot wallet that can be hacked.