Doesn't have to be someone at your work, it could be a block on a whole ISP network or at least an IP subnetwork that is shared between many clients

You can try emailing the address mentioned in their post so they adjust their filters to match just the bot networks more precisely

It might just be your corporate VPN and whatever ASN it’s being routed through.

You should file a support ticket with your manager and the IT security or support desk. Show them the evidence of 429s that are blocking your assigned tasks during working hours. Also include the screenshots and files that you downloaded on your personal device in order to access your work-related materials. Be sure and thank them for adequately configuring the MDM on your personal mobile device so that you could do these work-related tasks. You should definitely also file an expense report to request reimbursement of your personal mobile bill, any data charges incurred, and the hours of networking or collaborating with external colleagues, while you were working on these work-related projects with your personal device.