The "V" sound in "StePHen"

Not a PH, but the BH in Siobhan is pronounced with a “v”… would that be related?

Nah, that’s just because someone once decided to use silly nontransliterable* letters to spell Celtic words with our alphabet. We hates them, we does…

The “ph” in Stephen comes from Greek, not Celtic.

*I don’t think that’s a real word, but I’m not sure what it should be. The letters in Celtic writing (often) don’t signify the same sounds they make in English.

When he was a kid, we always called my nephew “Step-Hen”.

In Old English, they had the sound of [v], but it was considered only an allophone of /f/. The letter <v> didn’t exist yet—it was a French import into Middle English. In Old English the /f/ was pronounced [v] whenever it came between vowels (or between a vowel and a sonant, I think). The speakers of Old English did not think of [v] as a separate sound of its own, but only as a form of /f/.

“eraser” is not an exception for me. Both the verb “erase” and the noun “eraser” have a [z].

Oh. Let me substitute “racer”, then.

As is the MH in Niamh

Isn’t the name “Esteban/Estevan” the Spanish equivalent of “Stefan/Stephan/etc.”?

Perhaps it’s a mix of those sounds?

Nontransliterable is a fine word, and anyone who says otherwise will be beaten with a cudgel. It is composed of standard word elements; its meaning is clear from context. Admittedly I might have placed a hyphen between the first and second syllables, but I’m a Luddite. 18 points.