The Phage Cookbook by Dominik Refardt
Add 500 µL SMG and 25 µL chloroform to a 1.5-mL tube. Cut off the end of a blue (1-mL) pipette tip to make the bore wider and use it to core a single plaque from a plate (stab the tip vertically, then tilt the tip lift the cored plaque out of the plate). Transfer it to the tube (be careful when blowing the cored plaque out, as droplets can splash out of the tube). Flicker the tube and place it in the fridge for a couple of hours (overnight), to allow the phage particles to diffuse out of the plaque. A single plaque of phage λ yields about 106 phage particles.
Plate between 104 and 105 phage on soft agar (even 106 if they make small plaques). Incubate at 37 °C for about 6 hours (or until confluent lysis occurs). Add 5 mL SMG to the plate, seal with parafilm (to prevent accidental spilling) and keep it in the fridge overnight. Next morning, collect the SMG from the plate, add 50 µL chloroform and centrifuge at maximum speed for 5 min. Transfer the supernatant to a fresh tube and add again 50 µL chlorofrom. If things work nicely, you should get a titer of more than 1010 pfu/mL.
If you do it the first time, it can be helpful to plate several concentrations as well as only bacteria. The latter helps to judge whether lysis occurs.
Phages collected this way can be kept in the fridge for extended periods of time.