direct traffic based on information from the XML request

You can try this:

The pool member 8080 is assigned at the beginning... if msisdn is present and pool members are up, the pool member is changed.

when CLIENT_ACCEPTED { 
    set default_pool [LB::server pool]
}

when HTTP_REQUEST {
    pool $default_pool member 172.24.248.85 8080
    set msisdn [URI::decode [URI::query [HTTP::uri] msisdn]]
    switch -glob $msisdn {
        "*0" { set ports {8080 8180}}
        "*1" { set ports {8180 8080}}
        "*2" { set ports {8280 8380}}
        "*3" { set ports {8380 8280}}
        "*4" { set ports {8480 8580}}
        "*5" { set ports {8580 8480}}
        "*6" { set ports {8680 8780}}
        "*7" { set ports {8780 8680}}
        "*8" { set ports {8880 8980}}
        "*9" { set ports {8980 8880}}
        default { set ports {8080 8180}}
    }
    foreach port $ports {
        if { [LB::status pool $default_pool member 172.24.248.85 $port] eq "up" } {
            pool $default_pool member 172.24.248.85  $port
            break
        }
    }
}