RaspberrySnowCone welcome.
Social workers are not really scary people, IMHO, they are dedicated, hard working, sometimes late, often non-tea drinkers with amazing bladder control but not scary!
Re Can anyone shed any light on what is likely to be asked at that first phone call?
Probably why you want to adopt, whether you have any kids, if not the may ask if you have had fertility treatment and how long ago it ended. They may ask the type of accommodation you have, whether you have one or two spare rooms and whether you are interested in single child or sibling group, baby or older child or just open. If they only have older or younger or sibling groups they may want to make sure that they can actually take you on. If you are open it is helpful to say. They may ask your ethnic origin and if you have mixed heritage or different to white British heritage in your family it is useful to say as these types of adopters are very much sort after.
Re Will they take lots of notes or just a few and send forms? No idea, but they will probably invite you to an open evening or open day event which usually lasts one or two hours and is often held at the local county offices or their office and would be a time when they present to you the realities of adoption and where they give you a chance to ask questions etc.
Re Just really wondering if we need to so the call together or whether I can just ring to kick off the first stages?
Up to you but easer if you call as unless your other half is easily accessible during the daytime. If you have talked about the things mentioned above and know your joint family thoughts or at least an idea of them then personally speaking I think you can call alone. I know I did and my other half was fine because we had talked about it together before I made the call.
Good luck and please do keep us posted (great name, are you American?)