Well yeah, overclocking will be making your phone's CPU run at a faster clock speed than usual, increasing the chance for instability. It also will result in more heat. Components inside any smartphone are packed very tightly together with little open spaces for air ventilation (with the trend being waterproofing so essentially no ventilation). That leaves heat buildup a major problem, as even in just normal use without overclocking a phone can get warm.
<br> I'd recommend doing your overclocking in incremental steps over a few days and when it gets too warm or becomes unstable during day-to-day use crank it back a step or two.