Updated:

Breaking news:
The judge presiding over Jun Lozada’s case (“P vs. Lozada” for perjury) was about to say he might or he could issue subpoena to produce the President in court when he was cut off (ANC remote live interview) to give way to a studio guest waiting on cam.
Updated: The judge was giving an exclusive live remote interview ( just chanced upon it, not familiar with the perjury case filed against Jun Lozada by Mike Defensor, and have not read the order of the judge asking the parties to settle) to an ANC reporter, where he said that Malacañang had put pressure on him to recuse himself from the case but refused to give details (the “who”, “when”, “where”, “how”, etc.), saying that the emissary would just deny it. He then talked about the demolition job going on against him. Into 20 minutes of airtime he meandered into the following (i’m paraphrasing from memory): “masyado tayong naaaliw ng mga pangyayari, may kasal nila Mar Roxas at Korina, mga kandidato, etc (“we’re being entertained too much by events, the coming wedding of Mar Roxas and Korina, and the candidates, etc.”) hindi natin napapansin, baka mag-martial law na… (“it is escaping our attention that martial law could be declared…”) kasi baka dito sa kasong ito, bagamat….may mga nabasa naman akong pwede… baka ipatawag ang Presidente sa korte, may mga nabasa ako…. (because in this case…..i’ve read some materials that it can be done… the President might be summoned to court, i’ve read…..), then he was cut off by the news anchor at the studio because there was a studio guest waiting on cam.
The judge did not use the word “subpoena” and “arrest warrant”, but he was meandering towards that: subpoenaing the President or FG and, upon their refusal, issuing arrest warrants.
As we all know, there is no trial yet; preliminary motions have been filed.
You usually issue subpoenas on motion. At pre-trial you provide a tentative list of witnesses (among other things). In the course of the trial, you can add witnesses, or not use those in the list. When you have the trial dates, you ask the court, if required (like — if the witness requires it or the witness will not go with the lawyer, he/ she has to be subpoenaed), to issue a subpoena for the witness. Subpoenaing the President? Let’s see.
But hey, the judge is talking, we’ll just let him. If he cannot cite in contempt the public official who pressured him, maybe he should…subpoena the President? Cite her in contempt upon refusal? Have her arrested? If you couldn’t cite the President’s alleged emissary- influence peddler, sure you could cite her.