From what I hear, smart phones are like cpu mining on an Intel atom. Not very efficient. Supposedly you can mine with minergate on your phone but they take a bigger share of your profits than traditional mining. I would be worried about the cooling and degrading your phone.
Maybe put your phone in a zip lock bag and keep it in a liter of water in the fridge??
I'm concerned about phone degrading too. But it's same with desktop mining, the hardware does degrade overtime. '^'
I haven't been mining for very long but having gpu fans to 70%, undervolting, underclock shouldnt be too bad on the card. Running long hours in high temps causes wear on the components. Fans spinning really high can wear them out too. But if the fan goes you can replace them.
If you're limited on resources it's best to be cautious and make passive income rather than greedy and maxout your card. Don't make gpus cry