Is it permissible to convert an installment sale of a phone with deferred payment into an installment sale with an increased price when the buyer fails to pay on the agreed-upon date?

It is not permissible to delay a debt in exchange for an increase in money, because it is a form of riba (usury/interest) of Jahiliyyah (pre-Islamic era) which Allah has forbidden in His saying: "O YOU WHO HAVE BELIEVED, DO NOT CONSUME INTEREST, MULTIPLIED MANIFOLDS" (Quran 3:130). In Jahiliyyah, when the due date of a debt arrived, a man would ask the debtor to delay the payment in exchange for an increase in his money, and this is what Allah has forbidden.