Motivated by the growing demand for rare earth elements (REEs), it is crucial to design effective adsorbents capable of separating and reclaiming REEs from acidic wastewater. Herein, a phosphorus-functionalized covalent organic polymer (β-HCCD) was successfully synthesized via a straightforward nucleophilic substitution reaction, utilizing two cost-effective monomers β-cyclodextrin (β-CDs) and hexachlorocyclotriphosphazene (HCCP). Owing to the presence of abundant P-O bonds in β-HCCD and the unique cavity structure of β-CDs, β-HCCD exhibits adsorption efficiency exceeding 98% for scandium ions (Sc³⁺) within acidic solution with the hydrogen ion concentrations ranging from 5 mol·L-1 to 10⁻5 mol·L-1. Meanwhile, the complete capture of Sc3+ by β-HCCD can be accomplished within 2 minutes, and the adsorption isotherms demonstrated an outstanding alignment with the Freundlich model, exhibiting a maximum adsorption capacity of 101.0 mg·g⁻¹. What’s more, β-HCCD can be directly applied to industrial acidic wastewater without prior pretreatment, achieving an efficient recovery rate of 87% for Sc3+. These notable advantages including minimal expense, straightforward preparation process, fast adsorption dynamics and substantial adsorption ability demonstrate that β-HCCD holds significant promise for the recovery of REEs.