How to play an AMR file
An .amr file that will not open is almost never a damaged recording. AMR is a speech codec built for mobile networks, and general-purpose media players have long had patchy support for it — so a player with no decoder reports what looks, from its side, indistinguishable from a broken file.
Try a player that has the decoder
The shortest path is a player that ships broad codec support rather than relying on what the operating system happens to provide. VLC is the usual answer — free on every desktop platform, and it carries its own decoders, so it does not depend on the system knowing what AMR is.
Two alternatives if that is not available to you: ffplay, which ships alongside ffmpeg and plays the file from a terminal, and most Android handsets, which handle .amr natively because the format came from mobile telephony in the first place.
If a second player opens the file cleanly, the file was fine and the first player was the problem. That single test resolves most of these situations and costs nothing.
What not to do
Two common instincts make things worse.
Do not rename the file. An extension is a label. Changing .amr to .wav does not re-encode anything; it just invites a player to misread the contents, and it replaces an honest "I cannot decode this" with confusing behaviour.
Do not convert as a first move. Conversion produces a file that opens more easily and contains less. That trade may be worth making later for a specific reason, but it is a poor default — and if you make it, keep the original.
If the audio is evidence, treat the file as the artifact
Playing a file does not alter it. Editing, trimming, converting, or re-saving does — each of those produces a new file, and you then have two files instead of one.
The safe habit is simple: keep what you were handed untouched, and do everything else on a copy. It costs nothing and removes a whole category of later awkwardness.
If you opened it to find out what was said
Worth saying plainly: for a long recording, being able to play the file is not much of a win. A two-hour call is still two hours whether or not your player opens it, and listening is the expensive part.
If the reason you are opening the file is to find out what was said, transcribing it is the step that actually saves the time.
Questions
My player says the file is corrupt. Is it?
Usually not. A player with no AMR decoder often reports a codec it cannot read as a broken file, because from its point of view the two look the same. Trying a second player that does support the codec is the fastest way to tell the difference.
Should I convert it to MP3 so it opens everywhere?
Only if you keep the original. Converting produces a file that opens more easily and contains less than what you started with, because a lossy re-encode of already heavily compressed speech discards a little more each time.
Can I just rename it to .wav?
No. The extension is a label, not a description of the contents. Renaming does not change how the audio is encoded, and it usually makes things worse by causing a player to misread the file rather than reporting honestly that it cannot decode it.
Does playing the file change it?
Playing does not. Editing, trimming, converting, or re-saving does — those produce a new file. If the audio is evidence, keep the file you were given untouched and work from copies.