Dead Subwoofer output? (1 Viewer)

Hello everyone!
1st post here and I'm not terrible technical with this stuff so please bare with me. I have an older Denon AVR 1705, I'm using it to power some B&W speakers, DM 303s, DM 602 s3, a center channel I can't recall the model of and an asw300 sub. My question is, how can I tell if the subwoofer port is dead? Now Ive ruled out the sub as the problem, If i plug my iphone into the sub, headphone cable that splits into a Y, the sub works as it should. But when it's plugged into the port on the back of the Denon labeled "subwoofer" (think its called an LFE port?) I get nothing. I've gone thru and made sure all the speakers are set to small, I've set it to LFE + Main (which as I understand, means it should always use the sub).
I recently moved, but I was careful as I could be with this stuff so I don't think it got bumped around to much, is there any further tests I should be doing to confirm its the subwoofer port? Clearly the receiver is out of warranty, would this be a costly fix? I'm in a small town (Corvallis, OR) so my home theater options are limited.
Any suggestions would be great!
Thanks!
Jack

LFE + Main is a redundant useless setting(I wish it would go away)...
It isn't unheard of for a pre-out to crap out. And you are sure you turned the subwoofer to yes/on(whichever the setting is for Denon)?

Ah, forgot to mention that. I set it to "yes".
Off topic, but why is that setting useless? I don't know a ton about this stuff. just what I find on forums and random help articles.

LFE + Main is a setting intended to let the front speakers be set "large" but share in the bass management.
But "share in the bass management" is setting your front speakers to small.
So...
Large + "LFE + main" = small.
It was an appeasement done in the "infancy of 5.1" for those people that said...
"You know, this setting a speaker to small, for those people who buy big speakers is going to be confusing"...