Why does my font size randomly change in my text messages

[AC Question]

I have an LG Phoenix 2

 

[B. Diddy]

Welcome to Android Central! Which messaging app, the stock one? Do you mean that different messages have different font sizes, or that the font size for all messages will randomly change? On Samsung phones, the Vol button can increase or decrease font size in the messaging app -- does that work in your phone as well?