You do not go to prison for not committing a crime. There was no conspiracy found. And because there was no conspiracy found it is impossible to obstruct justice.
Haven't yet found the time to read the report? See
Mueller Report, Vol. II, p157:
Second, many obstruction cases involve the attempted or actual cover-up of an underlying crime. Personal criminal conduct can furnish strong evidence that the individual had an improper obstructive purpose, see, e.g., United States v. Willoughby, 860 F.2d 15, 24 (2d Cir. 1988), or that he contemplated an effect on an official proceeding, see, e.g., United States v. Binday, 804 F.3d 558, 591 (2d Cir. 2015). But proof of such a crime is not an element of an obstruction offense. See United States v. Greer, 872 F.3d 790, 798 (6th Cir. 2017) (stating, in applying the obstruction sentencing guideline, that “obstruction of a criminal investigation is punishable even if the prosecution is ultimately unsuccessful or even if the investigation ultimately reveals no underlying crime”). Obstruction of justice can be motivated by a desire to protect non-criminal personal interests, to protect against investigations where underlying criminal liability falls into a gray area, or to avoid personal embarrassment. The injury to the integrity of the justice system is the same regardless of whether a person committed an underlying wrong.
In this investigation, the evidence does not establish that the President was involved in an underlying crime related to Russian election interference. But the evidence does point to a range of other possible personal motives animating the President’s conduct. These include concerns that continued investigation would call into question the legitimacy of his election and potential uncertainty about whether certain events—such as advance notice of WikiLeaks’s release of hacked information or the June 9, 2016 meeting between senior campaign officials and Russians—could be seen as criminal activity by the President, his campaign, or his family.
Third, many of the President’s acts directed at witnesses, including discouragement of cooperation with the government and suggestions of possible future pardons, occurred in public view. While it may be more difficult to establish that public-facing acts were motivated by a corrupt intent, the President’s power to influence actions, persons, and events is enhanced by his unique ability to attract attention through use of mass communications. And no principle of law excludes public acts from the scope of obstruction statutes. If the likely effect of the acts is to intimidate witnesses or alter their testimony, the justice system’s integrity is equally threatened.