I get tired of this question. Of course we have the evidence we need for a credible impeachment vote, because the phone call itself represents an egregious breach of his oath of office. But 'Impeachable' does not mean the same thing as successful, because the end goal is not just to present an impeachment motion.
Good prosecutors don't write up marginally adequate indictments and submit them fast. They write up thoroughly investigated and researched ones that anticipate any possible legal or factual concerns either a judge or Grand Jury may imagine. .
The Speaker has called for an investigation, a probe into whether the House should impeach this President. She has not decided to impeach. The House of Representatives will set up committees to call witnesses to testify. Trumpsters and GOP cannot stop them, no matter how desperate they are, and how much they whine. House committees will subpoena witnesses and documents to support the case for that vote. Trumpsters and the GOP cannot stop them or rush them. That committee will endeavor to develop a full, complete and airtight historic record of this man's high crimes and misdemeanors based on his recent breaches of office and they will develop a legal, moral and political case for removal.
Then they will decide whether they ought to take articles of impeachment that they write, and report them first to the House floor through a vote, and then the full House, including the President's supporters, will decide whether to impeach this President and prepare for trial. Maybe they will, maybe they won't. The Speaker is not prejudging those decisions.
Some people may not want a full complete historical record of everything this administration did. Nancy Pelosi does. Some people may not want to see those legal, moral and political arguments for removal, fully prepared and on display in that committee report. Nancy Pelosi does.
That's too bad for some people.