Your average mobile processor doesn't have anywhere near enough processing power to run a state of the art text to speech network in real-time. Most text to speech on mobile hardware are stream from the cloud.
That said, having only skimmed the paper I didn’t notice a discussion of the compute requirements for usage (just training), but it did say it was a 28.7 million parameter model, so I recon this could be used in real-time on a phone.
[0] judging by the videos of Dr. Sbaitso on YouTube, it was only one step up from the intro to Impossible Mission on the Commodore 64.