Do your calls that are troublesome originate in the same location?
(Are you in the same area when this happens?)

Have you tried calling apps (free) to see if that resolves the issue?
(These apps make calls via wi-fi, not cellular. This could rule out the device as having an issue.)

The microphone is located somewhere along the bottom of the device. (Holes are there to let sound reach the mic.) Are you covering this with your hand?

 

Do you have the phone in a protective case?
Who is your carrier?
Could be bad cell reception

 

It is T-Mobile.
I have them, and they are terrible.

Is your Zoom running over wi-fi?
That would explain why it works.

I have to rely on wi-fi all of the time, because T-Mobile service is basically nonexistant.

I used to have Sprint, and the service was great- then came the merger, and now service is total trash.
Most times, it is literally like I do not have a phone.

If you can afford any other carrier that does not use the T-Mobile system (be sure to check first!) I would highly recommend to switch.

If you can, have people with different carriers (AT&T and Verizon preferred) to stand right next to you and everyone compare signals.
This is not a perfect test, but if one (or more) of you don't have any signal (or very low signal) then that is a red flag right there.

In the mean time, there are great calling apps that use wi-fi.
Personally, I use Dingtone.

https://dingtone.en.uptodown.com/android

It offers a free, real phone number and I have used them for years.

 

I know that this is a bit old, but I've had the same problem for the 18 months I've owned the phone (2020 model).

• As far as the mic goes, I still have the problem using bluetooth earbuds or wired earbuds, so for me it's not the phone's mic.
• Like the op, I take most of my calls at home, where it happens on every phone call. I have found that if I move away from my desk/computer it seems a little better, but not completely gone.

I know that when I moved in here and had AT&T (10 years ago), the reception was horrible, so I switched to Verizon and it was never a problem. A few years ago I went with a cheap service that uses both networks, brought my old, cheap ZTE phone over, and still had no problems. For xmas 2020 I treated myself to this (unlocked) phone, and it has always been a problem.

Remembering that the only other Motorola I ever owned back in 2011 had horrible reception everywhere I went (and was returned), I've come to conclude that Motorola has some weak antennas that don't perform well where I live, which is essentially on the border between suburbs and rural. Maybe the towers are a bit further apart here and this phone doesn't pull the signal as well?