My mic is awful for calls but not voice recorder?

Here's an example from my friends voicemail I left

https://www.dropbox.com/s/le5dlsg07bwt1ax/vm1.amr?dl=0

Here's an example of me recording on the voice recorder

https://www.dropbox.com/s/52mz45dtkini73k/Not%20Muffled.m4a?dl=0

before you say it's the carrier, it's the same muffled quality when I record my voicemail greeting. SO what gives? How can I increase my clarity of my iPhone6 Plus?