It is hard to give much in the way of suggestions because you don't provide much information. When you talk about another bacteria, how related are these strains? Did you try a range of dilutions of your phage? Was this all spotting on overlay lawns? Provide some detail please. Also showing a few pictures would be helpful, sometime things that people thing are clearing spots are just water droplets or similar, and a picture can help us come up with suggestions.

Sorry for not being clear earlier. I isolated phages using a Vibrio parahaemolyticus clinical strain that is phage-deficient. Initially, I was able to recover them using the same isolate. However, after the purification of phage suspension, I did spot analysis, but I did not observe plaques on the VP clinical strain but did see plaques on an environmental isolate. Now, I am seeing the opposite result , the clinical strain is now again susceptible to the phages, while the environmental isolate is not showing plaques. I am trying to understand what could be reasons of this inconsistency. We didn't dilute the phage suspension for this particular assay. I am attaching an example picture of where I got the clearing,

Here is the picture

Your bacterial lawn looks good and your spots seem ok. But I would suggest that you take a few of your phages and prepare a series of 10-fold dilutions and then spot each dilution. At some point you should see individual plaques and then you know you have good phage and you will have the approximate titer. When you have large spots like that it is hard to ascertain whether the spots are just an effect of the buffer, or something slightly inhibitory, or phage. What is surprising to me is that all of your phages (I presume each is independent) are not fully lytic phage and if they were truly a population of different phage I would expect some to be lytic and some to be lysogenic giving you turbid spot like you observe.

Thank you very much for your feedback. I really appreciate it!