We present a genome assembly from an individual female Stelis phaeoptera (the plain dark bee; Arthropoda; Insecta; Hymenoptera; Megachilidae). The genome sequence is 301 megabases in span. Most of the assembly is scaffolded into 17 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 18.6 kilobases in length. Gene annotation of this assembly on Ensembl identified 9,850 protein coding genes.