On topic: I don't have any helpful advice for being able to have more comfortable sex with a large penis because my vaginal canal is naturally 'roomy' enough to do so without having to do anything.
Certain positions can be less comfortable because of the placement of my cervix in those positions but in those situations I just let him know about the discomfort in as sexy a way I can think of in the moment, or with my hands.. I'll place them on his thighs and tell him with my body language that he needs to take it a little easier.
Even though I truly think the original post was likely bullshit (14 inches? I'm not sorry but no) there are discussions to be had about how some women handle larger partners when they have physical challenges doing so.