Many individuals believe that if they meet the SPHR exam eligibility requirements, then they should start there. However, this assumption is both important and dangerous for three reasons:
If you take the SPHR and fail it the first time around, you'll have to pay a second exam fee to take it again. Starting with the PHR makes more sense. You gather your baseline knowledge in your brain and then can go round two with the SPHR on firm ground. Passing the PHR first and then taking the SPHR is a much better use of two exam fees, and most importantly, it spreads your learning out over an extended period of time, which impacts long-term retention for career application. At the end of the day, career progression really is the point of putting you through the process.
Depending on the amount of time that you have available to study, reaching for the SPHR first may make for an unnecessarily stressful exam preparation process. Unless you have unlimited time to study and very few other obligations such as work and family, spreading your certification over two exam windows is perfectly reasonable.
Rome wasn't built in a day, and neither is your career. Both exams require recertification credits with a goal of lifelong learning. Instead of recertifying your PHR exam with webinars and classes, take the time to study and successfully pass the SPHR exam. Renewal, refreshment, and most importantly, relevance are the keys to a successful career in HR, and this path allows for all three.