Agency side here, placed a few people at IBM over the last 18 months. I'm not an IBM internal recruiter but I hear the debrief from candidates after every step. Let me give you the honest picture of the IBM recruiter phone screen.
It runs 20-30 minutes. A dedicated talent acquisition person, not the hiring manager. The goals of this call: Confirm you actually exist and match your resume. Understand why you're looking (they note this, especially if you're currently employed vs. in transition). Get a feel for availability, location expectations (many IBM roles are listed as hybrid, they'll clarify what 'hybrid' means for that specific team), and whether your comp expectations are in the zone.
What they actually ask: Walk me through your background and what brought you to IBM. What specifically about this role interests you? (Generic answers get noted. Know what the team does.) What are your salary expectations? (They ask this early. Have a number or a range.) Do you have any upcoming conflicts, time off booked, or other offers we should know about?
That last one sounds innocuous but if you have competing offers with tight deadlines, flag it early. IBM's process can be slow. I've seen loops take 5-7 weeks from screen to offer. If you have an FAANG offer expiring in 3 weeks, say so.
What actually sinks the phone screen: Bad answer to the 'why IBM' question. They can tell when someone just applied to everything. IBM has a very specific identity as an enterprise software company with strong consulting roots. Reference actual IBM products or divisions (watsonx, IBM Consulting, IBM Z, Hybrid Cloud), otherwise it sounds like you googled them for 45 seconds.
Also: they take culture fit seriously. IBM has explicit values language around inclusion and they probe for that in subtle ways. Not trick questions, just things like 'tell me about a time you worked in a diverse team.' Have something real.