Pass Variabled in AGI

Hello,
I have php file in which i am able to pass ${CALLERID(num)}. I also want to pass data like M9121052470001254357. I tried entering ${UID} but is not passing to php. Kindly help.
I have php file in which i am able to pass ${CALLERID(num)}. I also want to pass data like M9121052470001254357. I tried entering ${UID} but is not passing to php. Kindly help.