I´ve been investigating (like Doc Sportello) and found some interesting information about the release dates of Paul´s trailers for his last 3 films:
(This info is about the official trailers, i´m not counting the teaser trailers release dates for There Will Be Blood or The Master)
There Will Be Blood (2007)
Release Day: December 26
Trailer Release: September 7
3 months and 19 days before release day.
The Master (2012):
Release Day: September 14
Trailer Release: July 19
1 month and 26 days before release day.
Inherent Vice(2014):
Release Day: December 12
Trailer Release: September 29
2 months and 13 days before release day.
So with these patterns i assume we can get a trailer for "Phantom Thread" 2 or 3 months before the release day, maybe late september/early october.