Pete, you could be describing one of my phals; it's doing the same thing. It's been in this condition for quite a while; if it were going to cause a problem, I suspect it would have already. The small lower leaf (actually, it's the middle leaf) is nearly split in half, but it's still green. I'm not doing anything special to it. I figure if it's healthy enough to grow a great big leaf, it's healthy enough to lose the smaller split leaf. I've got another big phal with two of its middle leaves (the biggest two, with a 17" span) being pushed and ripped away by the huge spikes and roots. I know, terrible problem, right? The leaves are half torn away and have been for months, and they're only now starting to look a little paler than the other leaves. When they go, they go. It's a huge plant; it'll be fine.
I wouldn't worry too much. I find the less I worry about the orchids, the better they grow.