Translation:This is the perfect phone for my grandmother.
Hmm... I cannot give you some exact rule, but a two-word sentence "To pies" does sound strange indeed. Although "To jest pies, a to kot" (This is a dog, and this is a cat" is better. I guess worth to pay attention to other examples you encounter, whether they contain "jest" or not. But "to" as "This is" should always have the possibility of being replaced with "to jest".
Just a question, but if "jest" would be optional in this sentence, how are we to know if it is implied in "To idealny telefon" or "jest dla mojej babci". Basically the difference between "This perfect phone is for my gramps" and "this is the perfect phone for my gramps"?
Well, you can be sure that it is the first option here, because clearly "to" is a dummy pronoun here and not a determiner. Why 'clearly'? Because "telefon" is masculine, so its determiner should be "ten". Only "Ten idealny telefon" can mean "This perfect phone".
If we changed the noun to something neuter, then it becomes more ambiguous... but still I think that the first interpretation is a lot more probable.