A.T. Robertson Commentary Acts 8:29

"And the Spirit said unto Philip, Go near, and join thyself to this chariot." — Acts 8:29 (ASV)

Join thyself (κολληθητ). See this vivid word (be glued to, first aorist passive imperative) already in 5:13; Luke 10:11; 15:15. Philip probably jumped on the running board on the side of the chariot.