I just heard a radio commentator specifically spell and, then, pronounce the topic word as fAHj. I have always pronounced it as fAj. (dictionary.com has [feyj] which seems close to mine.)
Does anyone out there pronounce it like the commentator?
Somehow the look of this word says  ah.  I am not surprised if many will pronounce it with  ah.
I've always pronounced it with a long "a" and have no plans to change. I learned the word "bacteriophage" long before I ever heard the shortened version, and I've never heard bacteriophage pronounced with anything other than a long "a" so I just assumed "phage" would be pronounced similarly. To my understanding, both words refer to the same thing (a virus that replicates inside bacteria).
I've never heard the ah version, but M-W lists both.
Glucophage is pronounced glue-c-fahj. I would use the fahj pronunciation,but I've heard few peope say it. I've never encountered phage by itself. Your mileage may vary. If I am paying the utility bill, I want an env-i-lope, if a beautiful woman were to hug me, that would be en-vell-ope, and to announce the winner, it's he ahn-vul-lope.Â
"Anyone who adds up a column of numbers twice and gets the same answer both times simply has no imagination" - Mark Twain. Not sure if the IRS agrees, but they frown on imaginative tax retutns.