Zoom has begun to require you to have either a Waiting Room or Passcode for all meetings.
With the Waiting Room, even with knowing the meeting ID, only the Host allows individuals into the meeting. With a Passcode, once individuals click on the link to the meeting, they then must enter the passcode (which is usually in the invitation email) to be allowed into the meeting. You may use either method or both. Any meeting created before September 27th, 2020, will automatically have a waiting room added to it.
Furthermore, when calling by phone, it is recommended to let the Host of the meeting know that you are calling in by phone. This way, the host is aware of the number that is calling and will not remove you if the number is unknown to them.