P deficiency comes with visible signs. leaves will look blue-ish, for example.
what may seem like a stoppage of growth is really just subtle fattening, often. Watch a time-lapsed video and see how the last bit is just buds slowly getting bigger... slowly is key word.
grab a leaf symptom chart - google image search or there is a link with useful spreadhseets, charts and what not in my GD profile main page. sort comments by date and it'll be at the top. if you don't feel safe doing that, google image has all the same stuff, except for the homemade spreadsheets, of course.
spreadsheet saftey -- never open an unknown spreadsheet that has a macro. by default programs will warn you about such a thing before opening. nothing i made has a macro. no vb code used. just simple formulas. fwiw.
After looking at diary -- don't confuse autumn colors with the P symptoms. that's genetics and/or temps at night being a bit too low. Your plant slook a bit light, but that could be the grow lights creating a false depiction. if you started to "flush" don't bother.. plants need building blocks to grow. if you take those away, growth will be even slower. if you dropped feed a bit recently, maybe go back to previous formula.
if you did nothing, look over last few weeks and see when it started to progress.. consider a different plan next time to pre-emptively provide what is missing here. using same products helps, but sometimes new products are easier to use, too, even if there's a bit of a learning curve due to the change.
pic 5 shows potassium deficiency too. So, get the pH set, see if that fixes it, but prolly needs a bit more of everything , but since close to end don't go overboard.