Noise induced hearing loss is common, but most often it's related to the duration of loudness over time. Yes, it can happen suddenly too. The fact that you noticed it right after exposure indicates that it's Sudden Sensorineural Hearing Loss (SSHL). Excess noise can cause SSHL, as can other things like flying when congested.

I'm sorry to tell you that noise induced hearing loss is usually permanent. You say some of it has come back and that you can use the phone. That's a good sign.

Sometimes steroid treatment can help bring back some of the hearing lost, but it should be done as soon as possible after the SSHL is noticed. It's been quite some time since you became aware of it.

Did you explain to the ENT why you need an appointment?