[Asterisk-Users] Passing Var to PHP AGI script

[Mike Roberts]

exten => auth_dial,1,DigitTimeout,5
exten => auth_dial,2,ResponseTimeout,15
exten => auth_dial,3,Read(dialed,IVR/en_enter_destination,0)
exten => auth_dial,4,agi(call_start.php|${dialed})
exten => auth_dial,5,dial(SIP/${dialed}@146.82.15.241)

I'm trying to get What they dialed put into the PHP script. How do I
get the contents of this variable in the php script?