Spencer sits next to 4 phonetic neighbors — Hunter, Carter, and Parker are the closest matches by sound. Most share Spencer's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"dispenser of provisions, household steward"
"little star"
"powerful warrior"
"delight, luxury"
"brave advisor"
"associated with the church"
"famous warrior"
"of Mars, warlike"
"Yahweh is God"
"young seal, seal-born"
"counsel's guardian"
"fair-haired hero; white warrior"
"descendant of Ceallachán"
"elf counsel, supernatural wisdom"
"river, great river"
"morning"
"noble Roman citizen"
"lion of God"
"healer (if derived from Jason/Kason)"
"colt herder, horse keeper"
Similar sound: These names share phonetic patterns with Spencer — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Old French origins, giving them the same cultural heritage as Spencer.
Rhythm: Spencer is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.