When you sample, this usually implies that you are acquiring data elements (probably in an array) at a certain time interval. LabVIEW is unusual in Programming Languages in treating Time as a major part of the language, probably arising out of its roots as an "Engineering Workbench" (look at the last two letters of "LabVIEW").
For acquiring data, LabVIEW provides a very useful data type, the Waveform, selectable as an output format by DAQmx. A Waveform is similar to a Cluster -- its major elements are T0, the time the (initial) sample was acquired; dt, the time (in seconds) between samples, and Y, a 1D Array of Dbl containing the samples. Note that using the Waveform type automatically bundles the units of Time with the sample.
When you do Frequency Analysis, you exchange Time for Frequency. As the relevant Time for the Sample is the time between samples, the relevant unit for Frequency is the sampling Frequency, 1/t0. If you use the Spectrum functions on the Waveform Palette and wire in a Waveform, it will return the df, the "frequency increment", equivalent to the lowest frequency in the analyzed signal (or 1/(total sampling time)).
Phase is dimensionless. Look at the function that returns Phase and see if it is expressed as "degrees" or as "radians" -- you can, of course, convert from one to the other by simple arithmetic.
Try to avoid Express VIs -- they tend to "hide too many of the important details" and use unconventional things such as the Dynamic Data Wire that only lead to more complications and obfuscations.
Bob Schor
Search LabVIEW like a graph! 
