This may help. This is only for Yamaha OEM pistons. If you are using aftermarket such as SPI or Weisco you'll need to go by the manufacturer's specs for end gap.
You should be able to get access to manuals by becoming a VIP member here. I don't know if they have the Phazer manuals but if not I may be able to upload it to this site. It is too large for an email attachment as it includes the original years as well as supplements for several subsequent years.
The taper is very slight and over exaggerated in the manual. You would see it if you used a micrometer. The OEM Pistons have a Yamaha number cast on the inside. I don't have access to one right now but 8V0 rings a bell for the Phazer.
Thanks for your help Northofsixty, I see the 8V00 number on the inside of the piston so I will be confident that I can get factory replacement rings for this engine and they are not aftermarket pistons.