Many people just run YouTube videos in background listening to the audio anyway.
You can always run a WordPress plugin like PowerPress to simplify delivery.
Use ffmpeg to compress your audios. Be sure to normalize both sides of your conversation, if you're having a conversation with a 2nd person. Normalize - setting audio levels of all channels to broadcast standard, which allows people to listen to many channels + they're all the same volume. Use ffmpeg for normalization too.
Likely these audios can be mixed down to mono + compressed to a low bit rate, like 128k or lower.
This makes audios very small, so you can self serve them right off your site, rather than using an external service which can be costly + require time to setup/manage + when these 3rd party services glitch out (are slow or offline), you'll rarely be able to tell + even if you could tell, nothing you can do when this occurs.
Best to always serve audios directly off your own site, because if your site is down, no one can navigate to your audios anyway.
If your site is up + a 3rd party audio/video service is slow or down, conversions may simply drop with no real indication why.