Phosphorylation of heptahelical receptors is thought to regulate G protein signaling, receptor endocytosis, and non-canonical signaling via recruitment of β-arrestins. We investigated chemokine receptor functionality under phosphorylation-deficient and β-arrestin-deficient conditions by studying interneuron migration in the embryonic cortex. This process depends on CXCL12, CXCR4, G protein signaling and on the atypical CXCL12 receptor ACKR3. We found that phosphorylation was crucial, whereas β-arrestins were dispensable for ACKR3-mediated control of CXCL12 levels in vivo. Cortices of mice expressing phosphorylation-deficient ACKR3 exhibited a major interneuron migration defect, which was accompanied by excessive activation and loss of CXCR4. Cxcl12-overexpressing mice mimicked this phenotype. Excess CXCL12 caused lysosomal CXCR4 degradation, loss of CXCR4 responsiveness, and, ultimately, similar motility defects as Cxcl12 deficiency. By contrast, β-arrestin deficiency caused only a subtle migration defect mimicked by CXCR4 gain of function. These findings demonstrate that phosphorylation regulates atypical chemokine receptor function without β-arrestin involvement in chemokine sequestration and non-canonical signaling. Display omitted •ACKR3 function was analyzed in β-arrestin- and phosphorylation-deficient conditions•Phosphorylation regulates ACKR3-mediated scavenging independently of β-arrestins•β-Arrestin signaling is dispensable for CXCL12 guidance of interneuron migration•Absence and excess of CXCL12 cause similar interneuron motility defects Saaber et al. investigate the phosphorylation dependence of atypical chemokine receptor function in vitro and in vivo, focusing on ACKR3 and interneuron migration. They show that while phosphorylation of ACKR3 is essential, β-arrestin is dispensable for optimum receptor performance. They conclude that receptor phosphorylation regulates ACKR3 independently of β-arrestin.