Since ICMP is layer 3 protocol , there is no source port and destination port.But for a Firewall to install session it needs source port an ddestination port.
The ICMp hearder has identifier and sequence number.
The SRX uses identifier as destination and sequence number as source port.
Hence you may use any random number for source and destination ports usually 1 and 1 would suffice when you use show seurity match policies and protocol as icmp.
Please Mark My Solution Accepted if it Helped, Kudos are Appreciated too