What to leave off
A short list of things that read worse on a phone: a dense schedule of other events, a long organisation biography above the promise, and any block of text that only makes sense on a wide screen. Also worth cutting are the audience and outcome lines people like to store in a field guests never actually see โ say who it is for and what they will leave knowing inside the description or an agenda chapter, where the words genuinely appear.
Then check it the way a guest will. Publish, open the link on your own phone from a chat rather than a browser, and read only what is visible before you scroll. If you cannot tell what the session is, when it starts and how to register from that first screen, the fix is on the page and not in the message.