Over the years, I've only 'captured' a couple of Phoenix's off the net. 1 I saved as a 1984 and neither have clearance lights.
Right now, clearance lights are legally required on new vehicles. I looked once to try to find out when they became legally required with no success. Kind of confusing is that different manufacturers seem to have adopted them in different years, so no real solid clues. As Linda said, Dolphins had them in 1979, Sunraders in 1983. Until your Phoenix, I guessed Sunrader hung on until the last minute before having to modify their molds. So my best guess was the start date for the new requirement was Jan 1st 1983. Now I'm not sure.
Something I'm pretty sure of is that if they're fitted, they've got to be working or you might get a ticket.