涂油于

• 涂(river; borrowed sound)PHONETIC
• 土(earth; soil; land)RADICAL

Coating is like river water overflowing across a surface, just as clay covers it.

• 氵(water; liquid)RADICAL
• 由(from; due to; oil (phonetic))PHONO-SEMANTIC

Oil is a liquid that flows from a natural source.

• 于(at; in (pictographic — curved stroke representing breath escaping))ASSOCIATIVE

Breath curves and escapes from a person, meaning 'at' or 'in' a place.