Purpose: Purpose consideration of role of phosphorus in iron alloys surface engineering and relations of the iron phosphides layers growth parameters in processes of phosphorising, phosphorcarburising, and phosphonitriding with their structure and properties. Design/methodology/approach: The layers were generated on a base of Armco iron and 0.4%C, 1.1% Cr steel as a result of annealing in a mixture of argon or carburising, nitriding atmosphere and phosphorus vapours in: temperature T = 700 - 1170 K, phosphorus partial pressure p = 0.1 - 20 kPa, process duration t = 3.6 - 21.6 ks. The diffusion layers were investigated by means of the methods: metallographic, X - ray structural analysis, microanalysis, Vickers and wear dry friction resistance tests. Findings: Formation of compact layer of phosphides with the adjustable relation of Fe3P to Fe2P was described; means of growth and kinetics of iron phosphides layers and phosphocarburised and phosphonitrided were explained, it was found that iron phosphides presence in steel surface increases its hardness and resistance to wear. Research limitations/implications: Research implications it was found that nucleation Fe3P crystals starts in areas of surface being found in a certain distance from iron grains boundaries and the growth process of iron phosphide continuous layers is an effect of iron diffusion through phosphide layer from the core towards the surface. In advanced phases of the iron phosphide layer growth, a gap between the layer and the base is created as a process of degradation of the base layer interface. Practical implications: it has found that the obtained layers are new kind of composites diffusive layers with iron phosphide particles generated as a result of phosphorising, phosphorcarburising or phosphonitriding with very promising tribobiological properties. Originality/value: An original value of the paper is description of the formation elementary processes, structure and properties of the layers.