phpinfo() is disabled like mail() is currently. I don't know why anyone would need phpinfo() because it just dumps the php configuration to the user. There's nothing else it can do.
I suppose you could buffer the output, do a search for some element within the output, delete everything that was supposed to be output, and then create some different output, but it really sounds inefficient considering there are many better ways to check if the function works. You'll probably have to dig through the source and fix it yourself.