Hi,
You don't say what you want to do with the phase information, e.g display on a meter, input to a computer etc, or the level and waveform of the signals.
The simplest device for measuring phase shift (particuarly on sine waves at moderate levels) is to use a double balanced mixer ( DBM ). Feed with two signals of the same frequency and level it will give a DC output proportional to the phase of the inputs.
Mini-Circuits make a range of DBM's the classic being the SBL-1 see
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**broken link removed** >
Some are designed for phase detector use <
**broken link removed** > but any will work. As you can see from the data sheet, they are just 4 diodes (Not a bridge rectifier, look closely) and two small transformers.
You can also use either of the detectors from one of the 4046 PLL devices, just ignore the VCO. See
http://www.fairchildsemi.com/ds/CD/CD4046BC.pdf Signals in on pins 3 & 14, output for phase detector 1 (EX-OR) on pin 2, Detector 2 on pin 13
For digitial signals use an Exclusive-OR gate (7486) this will give a output pulse with a width proportional to the phase of two inputs, This can be integrated (low pass filtered) with a resistor and capacitor to give a DC voltage.
HTH,
G8RPI.