Hi Chieko,
Thanks so much for reaching out!
As a first step, can you please update your Events Calendar related plugins and see if that helps to resolve the issue?
Also, this snippet only works to add a phone number for Tickets, not RSVPs.
You could create a free ticket (once your Event Tickets Plus functionality returns) and get the phone number to appear that way.
If you go to Events Settings < Licenses, do you see your Event Tickets Plus license entered there with Valid Key?
You can also try removing the license and then re-add and Save Changes
Let me know how that goes!
Thanks,
Jaime