You can call them abecedarian words.
Abecedarian is an adjective meaning "being arranged alphabetically". It comes from the Latin abecedarius, which means "alphabetical," based on the names of the first letters of the Latin alphabet.
For example, below are the terms mentioned in a personal site:
Abecedarian Words: Words with letters in alphabetical order
Strictly Abecedarian Words: Words with letters in alphabetical order without repetitions
http://www.tanyakhovanova.com/
It is also mentioned in this stackoverflow question:
Counting abecedarian words in a list: Python