It's not: in the formula they posted, phi is the "passthrough from tariffs to import prices". That's where the country's own tariffs are factored in. Or am I reading this wrong?
You're reading it wrong because it's nonsense
None of the values are related to their names in any way
> Parameter Selection
> ... The price elasticity of import demand, ε, was set at 4.
> ... The elasticity of import prices with respect to tariffs, φ, is 0.25. ...