Older model Cel-Fi systems boosted one or some/all of the UMTS (3G) channels from the Operator. But if the boosted channels just happen to be loaded up with traffic from other users when you call, the network might have your phone use an unboosted network channel if it was good enough and less loaded (so you would not see the boosted signals but your call goes through fine). This is normal and not a problem. The Cel-Fi boosted channels are still there and available, and the important thing is that your calls etc go through whether you see boosted signals or not. These older models also did not boost LTE channels, so an LTE capable phone in idle mode (not in a call) may not show any boosted 3G channels. But again when you use your phone, the network (with or without Cel-Fi) is designed to send your call or data session to the best usable channel as needed.
Newer Cel-Fi models (such as PRO/DUO) have more capacity and also support LTE, so chances are that all 3G/4G/LTE channels in your area are being boosted.