Re: POLICY BASED ROUTING USING DESTINATION PORT

Biggest cotcha: applying firewall modify rule should be:

set interfaces switch switch0 firewall in modify FTP

Moreover, you're using rule number 21, this is unrelated to ftp being port 21.  (but still fine)  

Current rule takes all UDP and TCP traffic whereas ftp is only tcp.

It filters on your default gateway1 address,  this will (almost) never be source of ftp traffic.

For forcing ftp clients to use route 1 

Note: I'm not sure PBR firewall rule is also handled statefull, so you might run into trouble for passive ftp , which uses unknown high ports for data transfer. So use activ ftp mode

set firewall modify FTP rule 21 description "FTP PBR"
set firewall modify FTP rule 21 destination port 20,21
set firewall modify FTP rule 21 protocol tcp
set firewall modify FTP rule 21 modify table 1