The most straightforward explanation for the phone being drooped/discarded along her known jogging route is that it happened when Sherri was abducted. Other explanations, while possible, IMO, begin to get less credible the more you examine them. But that's just my opinion.
If Sherri was abducted at home, I doubt the abductor took the phone with him and then tossed it. Possible, but not likely, IMO. Nor do I think Sherri planted the phone there. If she wanted to pretend an abduction took place, she could've come up with a much better plan, one less ambiguous. The idea that her abductor spent hours in her home before whisking Sherri away also seems far-fetched. Without evidence that some stranger was in her home, I don't buy it.
It also doesn't look like she voluntarily left with a secret lover. Surely, LE would've found phone records or texts that connected her with someone else. Her life, from what we've been told, was wrapped up in being a mom.
If she just left on her own, planning to start a new life alone, she didn't seem to prepare herself with money, clothing, transportation, etc. Possible, but not likely.
The other viable possibility is suicide. But why go somewhere and do it where she wouldn't be found? And why wouldn't she just leave the phone at home? Again, suicide is possible, but unless we learn something specific about mental health concerns, I think it's unlikely.
If we take the text to her husband at face value, she apparently planned to be home at lunchtime. She wanted to know if he, depending on his schedule, might be home for lunch, too. Keith didn't express any surprise about the content of her text. So, it must be something that happened from time to time.
If she was wrapping presents (plural), she may have noticed the time and figured, if she hurried, she could do a quick jog and get back before lunch. If, by then, she heard back from Keith, she could plan lunch accordingly (and finish wrapping the presents).
While out, some people cutting down a tree saw her jogging (around 11 am as reported by Keith). Then, sometime shortly before noon, she was abducted near the mailboxes, dropping the phone during the struggle. (LE would know if that was the last time her phone was used.)
Abductions can happen so quickly. If Sherri was caught off-guard, someone could have gotten her into a vehicle under restraint (perhaps threatening her with a weapon) in no time at all. Except for the phone and earbuds, she disappears without a trace.