The website lists the specific location of accessibility seating on each type of aircraft: https://www.jetblue.com/at-the-airport/accessibility-assistance/boarding-process-accessible-seating; I messaged JetBlue to request priority seating, and the agent sent me seat assignments in the chat.
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The website describes the measurements of restrooms on their planes: https://www.jetblue.com/help/restroom-info
The website offers a live chat for special assistance but no phone number. During the trip, a complaint resolution official can be requested at any time. After travel, Call 1-855-ADA-LINE (232-5463).