Don't put solder on that. It will go out of spec and stress what it's connected to. If other phones work fine and you want to use that one, replace the plug and maybe use a straight one. That looks like a 90* and probably sits in the socket exactly the same way every time and not distributing normal wear. They sell through dealers so contact who you bought it from but it doesn't sound like it needs it if other phones work and that plug has an obvious issue.