Optimum routing is OTP/LHR/HEL/LHR/JFK/PHX return for 1040TPs. If you decide not to go to/from HEL you can opt for OTP/LHR/JFK/LAX/PHX for 800TPs. Each route has their benefits, eg plane types, timing, lounges, terminal changes etc

You may want to consider the party plane as an option. Not aware of any restrictions on availability sobshpuld be good for most options at the moment.