The symbol of pi is the Greek letter "π", which is similar in pronunciation to the Chinese character "Pai". There are two ways to input pi on the mobile phone (taking sogou input method as an example):

1. Find the "symbol" in the lower right corner of the mobile phone input method, select "Greece" under the "symbol" option, and enter the selection "π".

2. In the input method, if you enter "Pai" with the full spelling input method, the "π" option will automatically jump out and you can choose to enter.

3. As shown below, the "π" typed on the mobile phone. Similarly, characters like "π" can also be entered in the input method according to the above steps.