“Proto-Sinaitic (also referred to as Sinaitic, Proto-Canaanite when found in Canaan, the North Semitic alphabet, or Early Alphabetic) is considered the earliest trace of alphabetic writing and the common ancestor of both the Ancient South Arabian script and the Phoenician alphabet, which led to many modern alphabets including the Greek alphabet.”
And here are more sources that confirm that:
Sinaitic inscriptions, also called proto-Sinaitic inscriptions, archaeological remains that are among the earliest examples of alphabetic writing; they were inscribed on stones in the Sinai Peninsula, where they were first discovered in 1904–05 by the British archaeologist Sir Flinders Petrie. Apparently influenced both by Egyptian hieroglyphic writing and by the Canaanitic writing system (1900–1800 bce; probably ancestral to the North Semitic alphabet), the Sinaitic inscriptions date from approximately the beginning of the 16th century bce. Although not fully deciphered, the writing system appears to be alphabetic rather than ideographic.
Sometime during the second millennium B.C. (estimated between 1850 and 1700 B.C.), a group of Semitic-speaking people adapted a subset of Egyptian hieroglyphics to represent the sounds of their language. This Proto-Sinaitic script is often considered the first alphabetic writing system, where unique symbols stood for single consonants (vowels were omitted).
The alphabet seems to have been invented just once, by Semitic workers in Egypt nearly 4,000 years ago. The script they devised, known as Proto-Sinaitic script, was an attempt to repurpose hieroglyphics for their own language.