fog up
phrasal verb with fog verb [ T ] uk/fɒɡ/ us/fɑːɡ/ -gg-
布满雾气，蒙上雾
If a glass surface fogs up, a thin layer of liquid develops on it so that it is difficult to see through.
I couldn't see a thing because my glasses had fogged up. 我的眼镜起了雾，什么也看不到。