DON'T, you'll break your smartphone unless you can make sure it won't get too hot.
Will it be possible to run it in the first place by the way?
Why shouldn't it? Apart from the question of whether it's wise to have a smartphone work 24/7, modern smartphones are pretty capable these days as pointed out by Farul.
although running a node is not such an intensive work but it is still a lot more work than a Smart Phone is designed to do. it is basically a 24/7 communication over the internet where you send and receive data. depending on your setting it can be a lot of it too so your phone can overheat. that has the possibility to damage your hardware but also it will definitely lower the lifespan of your battery.
I always considered smartphone to use for lightweight applications. I see kids play games in the phone which damage the battery lifetime for the phone also it damage the hardware too.
Anyway, I think I need to reshape the knowing that we can run a full node in a smartphone :
Does it worth running a full node to a $500 to $1000 worth of smartphone, considering the constant communication over the internet, power consumption, risk to damage the hardware?