The mitts will start popping Wednesday morning when Phillies pitchers and catchers assemble for their first official workout of the spring on the emerald fields of Carpenter Complex in Clearwater. The group of candidates vying for spots in the starting rotation will look familiar. While the club made upgrades in the lineup (Carlos Santana) and bullpen (Pat Neshek and Tommy Hunter), the rotation went untouched. Aaron Nola comes into camp deserving to be Gabe Kapler's first opening day starter. Jerad Eickhoff, Vince Velasquez and Zach Eflin will be looking to bounce back from late-season health issues, and Nick Pivetta, Jake Thompson and Ben Lively will try to build on valuable experience gained last season. Strike-throwing Tom Eshelman, the organization's minor-league pitcher of the year in 2017, will be someone to watch, as will other prospects, including Drew Anderson and Jose Taveras. Now, will there be a mystery guest coming to camp? Quite possibly. As new manager Kapler said last month, general manager Matt Klentak "is busting his ass every single day looking for every possible opportunity to upgrade our team from every perspective. That includes looking at every option possible for the rotation." Klentak has talked all winter about his desire to add a starting pitcher, but he has made no promises and his quest has come with qualifiers. He has been leery of the price tags attached to top free agents (especially in length of contract) and trade candidates (quality of prospects needed to acquire). Also, Klentak, still steward of a rebuild, has had to balance his desire to add a pitcher with the need to make sure there are innings and opportunities for the current group of young pitchers to improve and reach their potential. The glacial free-agent pitching market finally began to thaw over the weekend with Yu Darvish reaching agreement on a six-year deal with the Chicago Cubs. Jake Arrieta, Alex Cobb, Lance Lynn, Jason Vargas, Andrew Cashner, Chris Tillman and others should begin to follow as camps get set to open.