I don't even bother with a strong password in my phone... just a 4 digit pass similar to how you have to put usually 4 digits to unblock your phone card. Since you should never carry anything valuable in a phone, it seems enough. You don't want to forget the password. Leave the long passwords for PC.

Mobile wallets' only superiority against all the other wallets is that you can carry it whenever wherever and check your balance just as long as you have internet connection.
However, other than the risks provided by OP, phones are vulnerable to hacks like when you're connecting to a wifi from a public area. They can maybe access your phone and steal your funds from your wallet.

that was good warn and i have experience download mobille wallet from App Store because i want to use my smartphone for controling my bitcoin but my friend has told to me that those wallet are malicious wallet and he has save me and my bitcoin because i remove those application immediately and since that i was never interested to using wallet from App Store again

Mobile phones and the apps, specially for Android are still more vulnerable then computers. That is the reason to be more careful with Bitcoin wallets too. And it is wise to have some antivirus and anti-spy software installed. Malwares are another way that your coins coudl be stolen.

I knew about the firts one but the second one was a surprise.
I did not know they save those private keys to the cloud and it could make our wallets vulnerable to hacks. I basically only use xapo app as I don't trust other wallets but I am aware of these wallets being more exposed to attacks due to mobile viruses.

Greenaddress can more or less be considered as a hybrid wallet. They do not store your mnemonic and thus have no access to it. They do create and send a password to the server and they will provide it only if the pin that the user set is correct. Without it, the mnemonic will remain encrypted. The pin was stored on Google's server encrypted.

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Smartphones are certainly not designed to be bulletproof against attacks since the OS is not really suitable for storing sensitive information. Phone wallets are good for paying conveniently while you're outside. Just be sure to treat the wallet as a day to day wallet and not store majority of your coins there.