Isogrammatic sentences?
A pangram is a sentence that uses each letter of the alphabet at least once.
- Pack my box with five dozen liquor jugs.
- How vexingly quick daft zebras jump.
A perfect pangram uses each letter of the alphabet exactly once.
- TV quiz jock, Mr. PhD, bags few lynx.
- Hjelmqvist-Gryb-Zock-Pfund-Wax
An isogram (or heterogram) is a single word that uses each letter at most once.
- uncopyrightable
- subdermatoglyphic
But what word/phrase describes a sentence that uses each letter at most once?
- Bide my frog’s quack.
- Jaws flunked copyright.
- Put back my English word!
Surprisingly, I can’t find any reference to sentences of this type either in a quick scan of Word Ways or in Ross Eckler’s Making the Alphabet Dance.
Going by Wikipedia, the OP's definitions are a little too strict.
Heterogram:
A heterogram (from hetero-, meaning "different", + -gram, meaning "written") is a word, phrase, or sentence in which no letter of the alphabet occurs more than once.
Isogram:
An isogram (also known as a "nonpattern word") is a logological term for a word or phrase without a repeating letter. It is also used by some to mean a word or phrase in which each letter appears the same number of times, not necessarily just once.
Ergo, it appears that the answer to the question is either heterogram or isogram depending on how pedantic one wants to be.
I don't know that I have an answer for you other than that this may be a situation in which a word needs to be invented. Here is my stab:
- Gram is a suffix that refers to something being drawn or written.
- Pan is a prefix meaning all.
- Iso is a prefix meaning equal.
Thus, a sentence which uses each letter within it only once would then follow to also be described as an isogram. However, since defining both phenomena using the same word may be confusing, perhaps a phrase such as "complex isogram" is in order. Better yet, perhaps it could be considered a unigram.