My Apple ID is gmail but it’s showing my mobile no.and I’m not able to activate iCloud but I’m able to download from apple store.

Hello Yak137,

We understand that you have some concerns regarding your Apple ID. Now, under things such as iMessage settings and FaceTime, it will show your mobile number as somewhere you can be reached. That's shown here: Add or remove your phone number in Messages or FaceTime

When you say that you're seeing your mobile number, where was that displaying? Please don't include screenshots including personal information, as we don't need to know your ID, but we just want to clarify where you are seeing a number as opposed to email.

Thanks!