Any method of estimating phage titer that is based on spectroscopic methods can only be reliable if the sample contains highly purified phage, preferably purified by CsCl gradient ultracentrifugation. Otherwise, other contaminating species (DNA, RNA, protein etc.) will lead to overstimation of the phage titer. A more reliable method would be qPCR.

I agree with Pierre Béguin that you would need to use highly purified stocks which will take much much longer to make than a simple plaque assay. Depending upon the accuracy you need, you can develop a spot titer method that only takes a few minutes to use and can read the results after 8-10 hours.

Also note that PFU may not be the same value as total virions, a physical measurement will give you how many particles you have, but PFU will tell you how many viable particles you have. These might be very similar, or might differ significantly, so it depends what you are intending to do.

Taqman base qPCR would give accurate virion count.

There are two most reliable methods

1. Plauqe assay

2.qPCR

3rd I never recommend is OD or spectrophotmetric based method .