To obtain Phnom Penh citizenship, you must first apply for Cambodian citizenship through naturalization. Key requirements include residing in Cambodia for a minimum of 7 years, demonstrating good behavior, and having knowledge of the Khmer language and Cambodian history. Additionally, submitting a completed application, supporting documents, and paying the relevant fees to the Ministry of Interior is essential. Please note that the process may be time-consuming, and consulting a local immigration expert for guidance is highly recommended.