In Greek mythology, Telephassa's claim to fame is that she is, going by the commonest version of the genealogy, the mother of Kadmos [Cadmus], who built the citadel of Thebes in Boiotia [Boeotia]; of Europa, after whom the continent of Europe was named; and of Phoinix [Phoenix]. She bore these children to her husband Agenor, the king of the region which would later be named Phoenicia, from their son Phoinix, after he had succeeded Agenor on the throne.
As far as I have known, there is no ancient mention of Telephassa's own parentage, but according to the Wikipedia article on her, "She was the daughter of Nilus, god of the Nile, and Nephele, a soft cloud Oceanid." The source cited for this is Stephen Fry's book Mythos: The Greek Myths Retold. (See p. 182 of the 2019 Chronicle Books edition thereof, under the alternate title of Mythos: The Greek Myths Reimagined.)
According to Pherecydes, Agenor had two wives, the first of whom, Damno, was also his own niece, and is the one who bore him Phoinix. It was the second, named Argiope, who bore Kadmos and, according to Hyginus (Fabulae 178), Europa as well. This Argiope, says Pherecydes, was a daughter of the Nile River.
Even though no ancient source seems to do this, Robert Graves fairly explicitly equates Argiope with Telephassa, essentially saying that the former is an alias of the latter (p. 194 of The Greek Myths: Complete Edition, 1992, Penguin Books). And all of that being as it may, Argiope's mother is still nowhere mentioned.
The only interaction aside from any of the above that I have encountered between an Oceanid and the River Nile comes from Servius' Commentary on Virgil's Aeneid 4.250, which gives us yet another cloud-nymph, namely Chione, as the daughter of the River Nile and the Oceanid Callirrhoe.
One might perhaps assume that Callirrhoe is the wife of the Nile and/or that she gave birth to (at least some of) his other children, including Argiope, who (if we follow Graves) is = Telephassa. From there, one might grant that perhaps when Fry mentions Nephele here, he simply means "an Oceanid", since the word literally means "Cloud," and is a more generic term for this class of nymph, who personified the clouds.
Beyond all this attempted puzzle-piece-sorting, Telephassa's pedigree in Fry's Mythos seems to me very much like an innovation on his part, and an almost completely arbitrary one at that. Is there any ancient (or even mediaeval) source that explicitly names Telephassa as a daughter of Nephele (and of the Nile)?