I'm trying to set up the Wi-Fi on my Yealink phone so that I can work from home and the password for my internet has symbols in it such as a question mark. How do I type in a question mark using the number pad on the phone?

When you need to type in symbol such as “?” or “@” with phone, you can the input method to "ABC" or "2ab"  by pressing soft key, then press star (*) key on bottom left of the pad to select the symbol as you want.

VP59 , T58A with Camera , SIP-T58A , SIP-T57W , SIP-T54W , SIP-T53W , SIP-T53 , SIP-T48S , SIP-T46S , SIP-T42S , SIP-T41S , SIP-T40G , SIP-T40P , SIP-T29G , SIP-T27G , SIP-T23G , SIP-T23P , SIP-T21(P) E2 , SIP-T19(P) E2 , SIP-T33P(G) , SIP-T31(P)(G) , SIP-T30(P)