Could someone explain the pronunciation, when I click the word पहला, the voice pronounces it normally, but when the entire phrase is pronounced, the voice utters पहला as if though it were spelled पैहला with an ऐ, which is standard (or both?) Thank you in advance!
The second one is the standard.
The letter ह messes with the phonetic pronunciation of a lot of words (such as यह, बहन, महल etc). When the consonant ह is present between two अ-vowels, both these vowels take an 'e' sound. For example, in पहला, ह् is between the अ attached to प and the one attached to ह so both these अs are pronounced as 'e'. In the absence of this vowel change, the second अ in this word would not have been pronounced so the second 'e' sound is sometimes omitted. As a result, पहला is pronounced 'pehela' or 'pehla'.
This 'e'-sound is formally absent in Hindi but is the shorter form of the ए vowel (or sometimes, the shorter version of ऐ).