First the Greek text of the last part of Phil 4:5 is, "ho kyrios engus", = "The Lord [is] near". There is no variation between UNS5, NA28, Majority text, TR, Byzantine text etc.
Most commentaries (eg Ellicott, Pulpit, Barnes, Expositors, etc) offer one or both of two suggestions:
- The Lord is "physically" near meaning that an awareness of the presence of the Lord ennobles our behaviour as specifically listed in the first part of the verse. That is, "near" means "close" as per John 19:42, Mark 1:38, 6:36, etc. It has some precedents in: Ps 34:18, 119:169, 145:18, 1 Kings 8:59, Acts 23:11.
- The Lord is "temporally" near meaning that the Lord is returning soon which should modify and ennoble our behaviour accordingly. That is "near" means "soon". In this understanding, the phrase could be a translation of the Aramaic "Maranatha" as per 1 Cor 16:22. This meaning is the one listed in BDAG for Phil 4:5; eg, Matt 26:18, Rev 1:3, 22:10, etc. This understanding has precedents in: Zeph 1:14, Eze 30:3, Obad 1:15, Joel 1:15, 3:14, Zeph 1:7, Isa 13:6, James 5:8.
- BDAG offers a third possibility based purely on the meaning of the word "engus" which is "being close as experience or event", eg, Rom 10:8, Heb 6:8. I cannot find any OT precedents for this meaning.
Now to my personal preference/bias. I prefer the first meaning but would not exclude the second meaning at all. I think both should be kept in mind. [As a personal spiritual discipline I believe in "practicing the presence of God".]