Why would you set option 150? No tftp is needed with shoretel phones. Shoretel you setup the following DHCP option...
Setup option 156 ftpservers=xxx.xx.xxx.xx, country=1, language=1, layer2tagging=0, vlanid=1
Technically it should ignore the vlanid after the layer2tagging is set to 0 but the specified syntax is correct.
Just make sure you setup the IP Phone Map to map the IP address range that those phones will pull to a specified site.