I found this question about connection speeds. Not sure if it answers your question, but I hope it helps.
It says that if you have the right equipment, and you hardwire your Eero, your connection will be as fast as your ISP (Internet service provider) allows.
It also says that if you can’t hardwire your Eero, it’s ok because they are designed to deliver the fastest connection possible.
It’s intended use is to make your wifi faster and easier to connect and download things over.
If your phone is slow because of WiFi, then it probably will make it faster. If it’s slower because it’s older or for any reason not WiFi related then it probably won’t.