The morphology of the change from an original Hellenist Greek "υ", via Latin, to English "y" is evidenced in numerous modern "English" (adapted foreign) words.
The garble almost certainly occurred from the first appearance (cBCE 10th century) of Roman Latins, when they began trading, in Latin↔Greek, via Semitic-speaking TzurꞋi•ans and Greek-speaking Pūlossian maritime shipping fleets of the eastern Mediterranean Basin—​also about the time that historians estimate that 𐤑𐤓 (the TzurꞋi•an) eclipsed 𐤑𐤃𐤍 (the Tzi•yᵊd•ōnꞋi•ans).
Following this pattern induces that prior to the "Greek Dark Age" 𐤑𐤓 would have been transliterated in Greek as ΘΥΡΑ. Around BCE 10th century Latin garbled ΘΥΡΑ as "Tyrus". The missing Latinized Greek transliteration-garble link in this pattern, from Greek ΘΥΡΑ at the beginning of the Greek Dark Ages to Semitized-Greek Θήρα (upper case ΘΉΡΑ —​Thera and Latinized-Greek "Tyrus", leading to Engish Tyre.
"Santorini (Greek: Σαντορίνη, pronounced [sandoˈrini]), officially Thira (Greek: Θήρα [ˈθira]) and classical Greek Thera"
Thira likely hearkens from a Greek Dark Ages
Since both Greek and Latin speakers simply knew the Semitic "foreigners" from the Greek "Phoenicians"—Latin Poenicus, they probably had no interest in transliterating from the Semitic 𐤑𐤓. The Latin populous simply "recognized" the Greek Υ as obviously a Latin "y".
English, which uses Latin letters, often adapted Latin stems with small grammatical changes. Thus, English retained the Latin "y" in these cases.
| Yirmeyahu Ben-David. U to Y Morphology (last update). Netzarim Jews Worldwide (Ra'anana, Israel).|
https://www.netzarim.co.il/Shared/Glossary/U-Y morphology.htm.htm (date accessed).