Hat tip to Daniel - MI0DNL/EI8ICB for the details

My rewrite rules are as follows - they go in the DMRGateway config file (access via the Expert editor in Pi-Star):

For Brandmeister:

PassAllPC0=1
PassAllTG0=1
PassAllPC1=2
PassAllTG1=2

These lines effectively mean “anything that hasn't been specifically directed to go elsewhere goes to Brandmeister”

For Phoenix:

TGRewrite0=2,8,2,9,1

This line means “any traffic on RF DMR timeslot 2 talkgroup 8 goes to/comes from Phoenix DMR timeslot 2 talkgroup 9, and do this only for this one talkgroup”

TGRewrite1=2,8000001,2,1,999999

This line means “any traffic on RF DMR timeslot 2 talkgroup 8000001 goes to/comes from Phoenix DMR timeslot 2 talkgroup 1, and do this for 999999 consecutive talkgroups (i.e. RF 8000001-8999999 map onto Phoenix 1-999999)

PCRewrite0=2,84000,2,4000,1001

This line means “private calls to reflector 84000 on RF DMR timeslot 2 go to/come from reflector 4000 on Phoenix DMR timeslot 2, and do this for 1001 consecutive reflectors (i.e. RF 84000-85000 map onto Phoenix 4000-5000)”

Use is as follows:

• Brandmeister - business as usual
• Phoenix reflectors - traffic goes on talkgroup 8 (instead of 9), and to connect just preface with an 8
• Phoenix talkgroups - just add 8,000,000 to the talkgroup number

• One thing to remember is that Phoenix uses TG400, not TG4000, to disconnect talkgroups - so if you're creating a Phoenix Talkgroup disconnect channel, it's TG 8000400 (eight million four hundred), not TG 8004000 (eight million four thousand)
• Disconnecting a reflector is a private call to 84000 (eighty four thousand)
• For anyone looking to add more networks to DMRGateway, the three prefixes that definitely won't conflict with any Brandmeister 7-digit talkgroups (as no DMR IDs exist beginning with these numbers) are 1, 8, and 9
• If you need more prefixes, knowing how DMR IDs are assigned will help you prioritise - the first digits are as follows: 2 is Europe, 3 is North America/Caribbean, 4 is Asia/Middle East, 5 is Oceania, 6 is Africa, 7 is South/Central America. So for an English speaker, the ones that'll cause the least conflicts with talkgroups you might actually want to use will probably be 4, 6 and 7.
• If you have a specific BM 7-digit talkgroup that conflicts with another network, you can map it elsewhere by adding something like the following line to Brandmeister (this would map the OARC bridge onto TG 20):

TGRewrite0=2,20,2,2348479,1