The who? Why? What are we thanking them for?
The phrase "Thank the Phoenicians" appears on various t-shirts and other places where catchy phrases are printed. The full phrase is, If you can read this, thank the Phoenicians. This is a line from the Epcot Center iconic ride Spaceship Earth. On that ride, you're taken through world history and it's stated that the Phoenicians developed the alphabet, and thus "If you can read this, thank the Phoenicians." As a result, the phrase is closely associated with Disney and Disney World fandom, and if you see a t-shirt with this phrase, the wearer probably got it at Disney World, not a Mediterranean history convention. (In fact, shirts with this phrase usually also have the Epcot symbol, representing the geodesic dome housing the ride.)
It's worth noting that the alphabetic origin claimed in the ride is not actually 100% accurate, but it's true enough. Other cultures developed alphabets and writing earlier, but the Phoenicians were into trade, so their alphabet spread to their trading partners, giving us shared, consistent writing across numerous cultures.
Naturally, this shared, consistent alphabet evolved and diverged in these other places, and the original Phoenician alphabet isn't the modern alphabet we use. However, it was the basis for the Greek alphabet, which then gave us the Latin alphabet, which gave us the modern English alphabet -- which is also almost identical to the Spanish alphabet, the German alphabet, and so on.
The Russian Cyrillic alphabet comes from Greek without a stopover in Latin-land, so it's a little different from the alphabet of most Germanic language and Romance languages, but still derives from the Phoenician alphabet.
I suspect that meany of the East Asian alphabets were not much influenced by the Phoenicians, but the Phoenician contribution to modern language is still very significant, and it's at least true for this writeup that we should thank the Phoenicians.
Sources/Further reading
- About the phrase and Epcot: https://disneyaddicts.com/spaceship-earth-if-you-can-read-this-thank-the-phoenicians-275290/
- About the alphabet: https://en.wikipedia.org/wiki/Phoenician_alphabet
- chromaticblue 's Phoenician writeup also covers this alphabetic origin.