Nomophobia, or the anxiety of being separated from one's mobile phone, is an emerging psychological condition in our digital age. The 20-item Nomophobia Questionnaire (NMP-Q) was developed to assess nomophobia symptoms. This study utilized item response theory (IRT) and classical test theory (CTT) methods to evaluate the NMP-Q's psychometric properties. Data were collected from 5087 adults who completed the NMP-Q. The CTT analyses included the computation of correlation coefficients, including McDonald's omega, Cronbach's alpha, Guttman's lambda 2, Guttman's lambda 6, greatest lower bound, average interitem correlation, Feldt-Gilmer coefficient, Feldt-Brennan coefficient, and Raju's beta. IRT analyses included graded response modeling of items, test information function, differential item functioning, and reliability. CTT analysis revealed high reliability coefficients across nine metrics and a four-factor model with good fit indices. IRT analysis showed a strong item fit to the polytomous graded model, indicating the questionnaire's robustness. Based on IRT (both uni- and multidimensional IRT) analyses, we propose a 10-item short version (NMP-Q Short), demonstrating high correlation (r = 0.97) with the original NMP-Q. Our findings provide very good support for the NMP-Q's reliability and construct validity. The items displayed good discrimination and difficulty parameters. The second 10 items of the NMP-Q appeared to be the most informative. The proposed NMP-Q Short offers a valuable option for efficient/rapid and accurate screening. However, additional validation and sensitivity testing are warranted to further establish its usefulness.