Mobile phones significantly improve access to healthcare, public health services, and disease surveillance globally. However, challenges related to reachability and accessibility persist, especially when individuals change or drop telephone numbers affecting continuity in public health interventions such as HIV follow-ups and vaccine reminders. We explored trends in phone ownership, changes in mobile phone numbers, associated factors, and the time it takes to better understand how these might affect the ability of phone-based public health services to reach targeted recipients. We used data from the Rakai Community Cohort Study, a population-based prospective open cohort in rural Uganda. Between 2010 and 2020, data on phone ownership and individuals' phone numbers were collected for six consecutive visits. We assessed trends in phone ownership using descriptive statistics. Factors associated with the number of times individuals changed their phone numbers were assessed using a Poisson multivariable regression model. We used Anderson Gill Cox proportional hazards regression to evaluate the time-to-change of phone numbers. In total 41,922 participants contributed 97,034 visits. A majority (61.8%) of participants owned a mobile phone at some point from 2010 to 2020. Phone ownership increased over the study period from 51.2% in 2010 to 68.2% in 2020 (p < 0.001). Phone ownership was lower among women participants (versus men; adjPR = 0.81; 95% CI 0.78-0.83) and younger persons < 25 years (versus ≥ 25 years; adjPR = 0.69; 95% CI 0.65-0.72), but there were no differences by HIV serostatus. The rate of change in phone numbers was significantly lower among women participants (adjusted prevalence ratio [adjIRR] = 0.88; 0.83-0.95) and those with secondary education or above (versus primary or none; adjIRR = 0.92; 95% CI 0.87-0.98). In contrast, it was higher among young persons aged 15-24-years old (versus 45 + years; adjIRR = 2.52; 95% CI 2.13-2.76), those living in lake Victoria fishing communities (versus trading centers, adjIRR = 1.28; 95% CI 1.17-1.40), persons with lower SES (versus higher SES; adjIRR:1.30; 95% CI 1.19-1.42), and persons living with HIV (versus HIV negative participants; adjIRR = 1.11; 95% CI 1.03-1.20). In this Ugandan cohort, mobile phone ownership increased over time, although by 2020 nearly 30% of the population still did not own a phone, and participants frequently changed phone numbers. Being a man, living with HIV, and lower socioeconomic status were all associated with changing phone numbers, a community peer system to maintain contact with these groups may be required to supplement phone-based initiatives.