Q. [ɸ], [β] became [f], [v]; [ɸ|β] > [f|v]
In Quenya the bilabial spirants ꝑ, ƀ [ɸ, β] (as derived from primitive ph, b) both became labio-dental f, v. These sound changes were mentioned in both the Outline of Phonetic Development [OP1] from the 1930s and the Outline of Phonology [OP2] from the 1950s:
ph: produced a bilabial spirant [ꝑ] ... Later or Tarquesta changes. ph > ꝑ became the labio-dental f (OP1: PE19/30-31)
ph became a bilabial spirant [ꝑ]. Later where preserved this became labio-dental [f] (OP2: PE19/71).
b became ƀ (bilabial v). Later, where preserved, ƀ became labio-dental v (OP1: PE19/32).
b became bilabial ƀ. Later, where preserved, ƀ became labio-dental v (OP2: PE19/69).
Examples are numerous in all conceptual periods. In the Late Quenya of the 1950s and 60s, the same developments applied to ƀ derived from w (OP2: PE19/72), but in the 1930s w > v occurred after the shift of ꝑ, ƀ > f, v (OP1: PE19/33).
In notes associated with the Shibboleth of Feanor, Tolkien indicates the ꝑ > f shift was fairly late, probably early in the TQ period but before þ > s, and that this sound change did not occur at all in the Vanyarin dialect:
It would appear that for reasons not now, of course, fully understood, the majority of the Ñoldor developed a distaste for the sound þ. This in Quenya was earlier, as it remained in Vanyarin, a dental spirant (made with the tongue-tip behind the back of the upper front teeth, which makes the passage to s easier). Similarly the labial spirant f was bilabial, and so remained in Vanyarin. The shift from dental and labial þ and f to interdental þ and labio-dental f occurred first in Telerin. The labio-dental f soon spread to Noldorin. Probably because it helped to make f and the voiceless w (transcribed hw) of Quenya more clearly distinguished (VT41/7).
In a footnote to the above quote Tolkien said:
The Ñoldor, before they made the change, accused the Vanyar of confusing the two sounds. In fact if left to unheeded change they would probably have merged in Quenya hw. Their near approach (by slackening the spirantal friction of f) before the separation of Vanyar and Noldor is seen in the development of phu- > *hwu- > hu-, as in Quenya huine “gloom”, unrelieved darkness (as a night without stars or moon), Telerin fuine of same sense, Sindarin fuin “night”. Later when the merging had been checked in Noldorin it was one of Feanor's jests to declare that the Vanyar called his father Hwinwe and himself Hwëanaro (VT41/8 note #1).
Hit tip to Shihali for pointing out those to quotes to me. In OP2, Tolkien did not mention the preservation of bilabial f [ɸ] in Vanyarin, but he did say that hw > f in that dialect (PE19/75, 79, 88). This Vanyarin-only development is more plausible if f remained as bilabial ꝑ, so Tolkien may have established the TQ timing of ꝑ > f in OP2 or even in OP1.
Conceptual Development: Tolkien also described these sound changes for the Early Qenya of the 1910s and 1920s, except in the earliest conceptual stages bilabial spirants ꝑ, ƀ were part of Primitive Elvish (PE12/15, 20, 24).