I just tried my daughter's Fender mustang bass it's a PJ.I tried a Fender Mustang the other day and it had the same issue on the 15th fret of the E string.
The weather's changing here in the mountains so I did a quick trust rod adjustment with a feeler gauge .012 at the 8th fret with a capo on the one and pressing down on the last fret.
And I did not have any phasing issues.
