What if you lose your phone, which happens...
I'd rather store it on a web wallet and upload the private keys to gmail.
It is beter to copy your private keys on paper wallets rather than upload it to gmail, IMHO.
Overall I think its pretty safe but keep in mind a paper wallet is of course way more secure, with a mobile its maybe pretty secure but it still can be hacked.
Of course paper wallet is way more safe but you can also not compare that in my opinion, I think that a mobile wallet is considered to be safe but I also think its depending on how you secure your mobile..
More safe, store your savings in paper wallets and use mobile wallet for daily spending just like your traditional wallet.