While Ephesians 2:18 is not a prayer, the access to God the Father is declared. I begin quoting Ephesians 2 with verse 13 and part of 14 so that you can see that “Through Him” is a reference to the Lord Jesus Christ. It says: “But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ. For he is our peace, who hath made both one, and hath broken down the middle wall of partition between us …. For through him we both have access by one Spirit unto the Father.”
So prayer is made “unto the Father” and it is “by” the Spirit, “through” the Lord Jesus. We pray through Jesus Christ, by the Spirit, unto the Father. Prayer is always addressed to God the Father.