There is no special term for such nouns other than noun phrases with postpositive adjective, a rather limited set which includes a number of non-count nouns (malice aforethought) and others where a plural would be automatic (women alone). Many of these nouns are legal terms inherited from French and Latin or fully English expressions like Princess Royal that nevertheless follow Romance syntax with the adjective usually following the noun.
Since in the entire history of the British monarchy there have only been seven princesses royal, including the current holder of the title, Princess Anne, it’s not a word whose plural is required very often except in statements like this one. The French word order is the work of the one who insisted the Crown create such a title for the eldest daughter of a reigning monarch, the French queen of Charles I, Henrietta Maria. All of the “generals” — attorney, consul, governor, paymaster, surgeon, vicar — form plurals in the same way.
Now when this French syntax meets the Saxon genitive, it’s a grammatical Waterloo: only two US Supreme Court decisions have ever used the form attorney’s general; the rest have resorted to attorney general’s or to what Fowler called the “Norman” genitive: of the attorney general.
The Attorney General's Office (AGO) provides legal advice and support to the Attorney General and the Solicitor General (the Law Officers) who give legal advice to government. — Attorney General's Office - GOV.UK
Merriam-Webster does allow attorney generals as a plural, but there is considerable resistance among the legal profession to the change.
To complicate matters, French and Latin noun phrases generally form their plurals as they do in those languages:
persona non grata personae non gratae
agent provacateur agents provacateurs
agente provacatrice agentes provacatrices
cause célèbre causes célèbres
femme fatal femmes fatales
A retired professor can also sport a gendered adjective: professor emertus, professor emerita, and if there's more than one, professors emeriti, professors emeritae.
As for what to call something like *phones mobile — why not completely cross the Channel with *phones mobiles? — I’d call that a humorous pseudoforeignism, like pronouncing the big box store Target as if it were the French name of some upscale shop.