Ok,
A Phasing cable is made of two 1/4 wave sections of 75 ohm  Coax.

2808 divided by frequency in MHz. = 1/4 wave in inches.

VF = Velocity Factor  (most 75 ohm coax the VF = 0.66)

Each one should be an odd number of 1/4 wave length times the VF

by adding a 1/4 wave length of 50 ohm coax to one side, makes a delay
line of 90 degrees.

Remember to factor in the connectors to the length.

To use the MFJ 259B,  437 MHz. divided by 3 = 145.6 MHz.
2808 divided by 145.6 = 19 1/4 inches. of 75 ohm coax.
connect one end to the MFJ set frequency to 145.6 trim
1/4 inch at a time until the Resistance Meter reads zero.
Then that should be exactly 1/4 wave length at 145.6 MHz.
And also 3/4 wave lengths at 437 MHz.

Good Luck

73 Al Lowe N0IMW