Are you sure that it is the antenna causing the problem?
Have you checked the signal strength bars on the phone when there is silence to see if the signal is lost?
Have you tried using the earphones with the microphone attachment to prove whether the problem is with the voice reception circuitry of the phone or whether it may be with the actual internal earphone receiver itself.
Have you tried it in loudspeaker mode?
Can the other people still hear you when there is silence at your end or is the call lost?
Here is a link to the antenna module part for your phone.
Here is a link to the Ifixit guide on how to replace the motherboard in your phone.
This is handy as it shows how to access the internal parts of the phone.
Nexus 4 Motherboard Replacement
If the people hear you in the silences that proves that the antenna is working.
You are losing reception only not transmission and it is the same antenna.
Does it also happen when using the external earphones/microphone? You didn't say.
Does the letter H stand for Headphones by any chance? If so it means that it thinks that the headphones are connected and that is why you are losing reception because it has switched over to the earphone socket. If the letter H doesn't mean this sorry to have led you astray.
If it doesn't happen when using the external earphones/microphone then I think that perhaps it may be a problem with the earphone socket.
Depending on what type of socket it is when you plug in headphones depends on what occurs.
There is the type where an internal contact in the socket itself makes and "tells' the controller to electronically switch the audio away from the receiver to the headphones. There is the other type where there are two sets of contacts in the socket which mechanically change the audio away from the receiver to the headphones.
If it still happens with the earphones/microphone have you tried a factory restore to see if it is a software or hardware problem? Backup your phone first before you do this. You can restore your phone later from the backup
If it still happens in default factory mode and also when using the external earphones/microphone them it could be either the module or the motherboard. It might be easier to change the antenna module first to prove it (depending on price).
If it doesn't happen when in factory default mode then it may be a downloaded app that is causing the problem, because in factory default mode it is only the basic operating system that is installed.